The present invention relates to a geothermal “direct exchange” (“DX”) heating/cooling system, which is also commonly referred to as a “direct expansion” heating/cooling system, comprising various design improvements.
Conventional and older design geothermal ground source/water source heat exchange systems typically utilize liquid-filled closed loops of tubing (typically approximately ¼ inch wall polyethylene tubing) buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged liquid transport tubing. The tubing loop, which is typically filled with water and optional antifreeze and rust inhibitors, is extended to the surface. A water pump is then used to circulate one of the naturally warmed and naturally cooled liquid to a liquid to refrigerant heat exchange means.
The transfer of geothermal heat to or from the ground to the liquid in the plastic piping is a first heat exchange step. Via a second heat exchange step, a refrigerant heat pump system is utilized to transfer heat to or from the liquid in the plastic pipe to a refrigerant. Finally, via a third heat exchange step, an interior air handler (comprised of finned tubing and a fan) is typically utilized to transfer heat to or from the refrigerant to heat or cool interior air space.
Newer design geothermal DX heat exchange systems, where the refrigerant fluid transport lines are placed directly in the sub-surface ground and/or water, typically circulate a refrigerant fluid, such as R-22, the like, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer geothermal heat to or from the sub-surface elements via a first heat exchange step. DX systems only require a second heat exchange step to transfer heat to or from the interior air space, typically by means of an interior air handler. Consequently, DX systems are generally more efficient than water-source systems because fewer heat exchange steps are required and because no water pump energy expenditure is necessary. Further, because copper is a better heat conductor than most plastics, and because the refrigerant fluid circulating within the copper tubing of a DX system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, generally less excavation and drilling is required (and installation costs are typically lower) with a DX system than with a water-source system.
While most in-ground/in-water DX heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements, particularly in direct expansion/direct exchange geothermal heat pump systems, are taught in U.S. Pat. No. 5,623,986 to Wiggs; in U.S. Pat. No. 5,816,314 to Wiggs, et al.; in U.S. Pat. No. 5,946,928 to Wiggs; and in U.S. Pat. No. 6,615,601 B1 to Wiggs, the disclosures of which are incorporated herein by reference. Such disclosures encompass both horizontally and vertically oriented sub-surface heat geothermal heat exchange means.
DX heating/cooling systems have three primary objectives. The first objective is to provide the greatest possible operational efficiencies. This directly translates into providing the lowest possible heating/cooling operational costs, as well as other advantages, such as, for example, materially assisting in reducing peaking concerns for utility companies. The second objective is to operate in an environmentally safe manner via the utilization of environmentally safe components and fluids. The third objective is to operate for long periods of time absent the need for any significant maintenance/repair, thereby materially reducing servicing and replacement costs over other conventional system designs.
Historically, DX heating/cooling systems, even though more efficient than other conventional heating/cooling systems, have experienced practical installation limitations created by the relatively large surface land areas necessary to accommodate the sub-surface heat exchange tubing. For example, with horizontal “pit” systems, a typical land area of 500 square feet per ton of system design capacity was required in first generation designs to accommodate a shallow (within 10 feet of the surface) matrix of multiple, distributed, copper heat exchange tubes. Further, in various vertically oriented first generation DX system designs, about one to two 50 foot to 100 foot (maximum) depth wells/boreholes per ton of system design capacity, with each well spaced at least about 20 feet apart, and with each well containing an individual refrigerant transport tubing loop, were required. Such requisite surface areas effectively precluded system applications in many commercial and/or high density residential applications. An improvement over such predecessor designs was taught by Wiggs, via the utilization of various DX system design features that enabled a DX system to operate within wells/boreholes that were about 300 deep, thereby materially reducing the necessary surface area land requirements for a DX system.
However, over the years, two common additional problems have been encountered with pit style DX systems, and with vertical well style DX systems.
First, a common problem with pit style systems is the easy ability for the geothermal heat exchange field to become “overstressed”, particularly in the cooing mode. An overstressed horizontal pit type DX system, which is well understood by those skilled in the art, can take weeks to return to normal temperature conditions if severely overstressed in the cooling mode. It is an object of the subject invention to provide a solution to this subject problem without the need for additional significant land surface area to increase the size of the horizontal heat exchange field, comprised of an array of tubing typically spaced 2 to 12 inches apart.
Second, a common problem with vertical well type DX systems is the periodic occurrence of the borehole partially becoming filled up with debris from the surface accidentally knocked into the hole, or with a partially collapsing wall depositing debris into the bottom of the hole, or with mud from a mud seam leaking mud, or the like, into the bottom of the well/borehole, or with debris being knocked into the bottom of the well during the actual sub-surface refrigerant transport, vertically inclined, geothermal heat exchange tubing/loop installation. A vertically inclined DX system geothermal heat transfer loop is well understood by those skilled in the art. Such debris is typically not discovered until the tubing cannot be extended to the full intended and originally drilled depth. It is an object of this invention to provide a solution to this somewhat frequent concern without having to completely remove the mostly inserted heat exchange tubing, and re-drilling the borehole to clean it out, which is both time-consuming and expensive.
A third problem common to the above DX system designs is a sub-surface suction line pressure loss, which can impair system operational efficiencies.
The present invention provides a solution to these preferable objectives, as hereinafter more fully described.